Atleast they could build one which non of the European countries have been able to do yet other than being allowed in the F-35 program but US at that Point have already had an even more advanced stealth fighter the F22.Using Chinese stealth technology is a bad example, because most of it was straight-up stolen from the Americans via corporate espionage. The PRC's acquisition of stealth jets was not due to its large population, for example, resulting in more skilled engineers, but a result of Chinese spies stealing American F-22 and F35 fighter tech.
It tell quite alot how far behind European countries have fallen in terms of military technology, they simply can't keep up in terms of cost and can't afford stuff like F22. China atleast have reached and will eventually surpass US economy output by a significant margin and like US can concentrate wealth on very expensive research Projects, something the smaller and poorer European countries have generally been unable to do.
So large population meaning technological backwardness don't make too much sense.